There are numerous processes directed to the manufacture of fluorinated organic compounds and to compositions containing such compounds. Many of these processes involve the reaction of an organic compound, such as a chloroalkane or chloroalkene, with hydrogen fluoride (HF) in the presence of a fluorination catalyst. In several of these processes, water is present in one or more of the reaction product streams containing the desired fluorinated organic compound. This water may originate as an impurity in the reactants or other starting materials. The water also may be formed as a byproduct from the reaction process, including reaction of HF with the catalyst, and/or as a product of the catalyst regeneration process.
It has been recognized that mixtures of water and hydrogen fluoride are especially corrosive, and that this combination is both difficult and expensive to handle. As a result, it is typically desirable to remove water from those portions of the fluorination processes where it is exposed to HF, including in product streams, byproduct streams, reactant streams, and recycle streams. Moreover, water which is present in the fluorination process, even at low levels, may act as a catalyst poison, thereby having deleterious effects on the effectiveness, efficiency, selectivity and/or yield of the fluorination reaction.
Several methods of removing or reducing the amount of water from fluorination process streams have previously been proposed. For example, U.S. Pat. No. 5,334,784 (Blake, et al.) and U.S. Pat. No. 6,103,944 (Blake, et al.), suggest distillation as a method for physically removing water from a fluorination process stream. U.S. Pat. No. 6,111,151 (Ewing, et al.) discloses phase separation as an alternative method of physically removing undesirable water from the process stream. In addition, drying agents such as sodium polyacrylate (U.S. Pat. No. 6,101,818, Thomas, et al.) and calcium chloride (U.S. Pat. No. 5,723,702, Kwon, et al.) have also been suggested as a means to absorb water from a process stream. While Blake, Ewing, and others in the field have attempted to remove water from the reaction product by using equipment and methods downstream of the fluorination reactor, such as those described above, these processes are inherently expensive. Moreover, known absorbents that are compatible with the fluorination reaction are not selective for water and therefore cannot generally be used to advantage during the fluorination process. Each of the aforementioned methods also pose a further disadvantage in that they can only remove water downstream of the process reaction, and therefore they are not effective for the removal of water at the reaction site and cannot prevent catalyst poisoning.
Process streams downstream of the fluorination reaction typically contain unreacted organic materials and unreacted HF in addition to the desired fluorinated compounds. To increase product yield, it is common to separate the unreacted starting components from the product stream and to recycle HF and/or the under fluorinated components back to the reaction step. Because recycling tends to increase the concentration of water present during the fluorination reaction, it is advantageous to remove any water from the product stream prior to recycling.